The Interaction of Porphyromonas gingivalis with Human Peripheral Neutrophils. Porphyromonas gingivalis is a gram negative anaerobic bacterium whose interaction with neutrophils (PMN) likely plays a role in the pathogenesis of periodontal disease. The aim this project was to investigate the role of opsonization in the interaction of P. gingivalis with human PMN. Cells of different P.gingivalis strains were mixed with PMN in PBS (pH 7.4), in the presence or absence of human serum (10%), known to contain antibodies to P.gingivalis. The reaction mixture was incubated 4 degree Celsius for 30 min. The PMN-P.gingivalis pellet was separated from unbound bacteria by centrifugation at 300g, then washed with PBS to remove loosely adherent bacteria . Adherence of P.gingivalis to PMN was assessed by enzyme-linked immunosorbent assay (ELISA) using anti P.gingivalis antibodies. Results (triplicate values q SD of absorbance at 405 nm) are shown below. Strain Serum No serum Bacteria alone 381 0.620 q 0.2 0.661 q 0.3 0.17 q 0.03 A7A1-28 0.881 q 0.22 0.916 q 0.15 0.15 q 0.06 W-50 1.471 q 0.12 1.00 q 0.10 0.11 q 0.06 To more precisely quantify these results a radioassay has been used. Bacteria are labeled with 3H thymidine during growth and bacteria bound to PMN are determined by low speed centrifugation and liquid scintillation. To date this assay has been used with strain 381 and the results confirm the above ELISA results for this strain. Key words: P.gingivalis-pathogenicity; Neutrophils; immunology, binding; Antibodies, bacterial- immunology; Bacteria, Pathogenicity